|Número de publicación||US8447508 B2|
|Tipo de publicación||Concesión|
|Número de solicitud||US 12/651,529|
|Fecha de publicación||21 May 2013|
|Fecha de presentación||4 Ene 2010|
|Fecha de prioridad||4 Ene 2010|
|También publicado como||CN102116371A, CN102116371B, DE102010055660A1, US20110166758|
|Número de publicación||12651529, 651529, US 8447508 B2, US 8447508B2, US-B2-8447508, US8447508 B2, US8447508B2|
|Inventores||Paul G. Otanez, Chunhao J. Lee, Farzad Samie|
|Cesionario original||GM Global Technology Operations LLC|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (25), Otras citas (7), Clasificaciones (20), Eventos legales (5)|
|Enlaces externos: USPTO, Cesión de USPTO, Espacenet|
This disclosure is related to a system and method for controlling the slip in a torque converter of a vehicle.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engine vehicles that employ automatic transmissions typically include a torque converter positioned between the engine and the transmission of the vehicle. A torque converter is a fluid coupling device typically including an impeller coupled to an output shaft of the engine and a turbine coupled to the input shaft of the transmission. The torque converter uses hydraulic fluid to transfer rotational energy from the impeller to the turbine. Thus, the torque converter can disengage the engine crank shaft from the transmission input shaft during vehicle idling conditions to enable the vehicle to stop and/or to shift gears.
The rotational speed of the impeller relative to the turbine in the torque converter is typically different so that there is a converter slip therebetween. Because large slips between the engine output and the transmission input significantly affect the fuel economy of the vehicle, some vehicles employ a torque converter clutch (TCC) for controlling or reducing the slip between the engine and the transmission. The TCC can also mechanically lock the impeller at the output of the engine to the turbine at the input of the transmission so that the engine and transmission rotate at the same speed. Locking the impeller to the turbine is generally only used in limited circumstances because of various implications.
Thus, a TCC generally has three modes. A fully locked mode as just described, a fully released mode and a controlled slip mode. When the TCC is fully released, the slip between the impeller and the turbine of the torque converter is only controlled by the hydraulic fluid therebetween. In the slip mode, the slip between the torque converter impeller and turbine is set so that it does not exceed a predetermine amount by controlling the pressure of the hydraulic fluid in the TCC.
In a torque converter with a TCC in slip mode, changes in conditions affecting the torque converter can cause increases or reductions in slip. For example, a change in engine torque can change the slip in the torque converter before commands to the TCC, including a time lag between the change in slip and reactions in the TCC to control the slip, can control the slip back to a desired or target value. As a result, transitions in the torque converter can generate unintentional changes to the slip. For example, an unintended reduction in slip to a low or zero slip resulting in a torque converter crash can result from an unintended reduction in slip. Crashes cause perceptible changes to the operation of the vehicle or cause drivability issues. Quick and accurate detection of a torque converter crash can be helpful to minimize adverse effects of the crash.
A powertrain includes an engine, a transmission, and a torque converter located between the engine and the transmission. A method for controlling torque converter slip includes operating the torque converter in a controlled slip mode, monitoring slip in the torque converter, statistically analyzing the monitored slip to determine a likely condition of the torque converter, and utilizing the likely condition of the torque converter to control the torque converter slip.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The vehicle 10 also includes a controller 36 intended to represent both an engine controller and a transmission controller; however, it will be appreciated that these two controlling functions can be served by a single device or a plurality of communicatively connected devices. The controller 36 receives a throttle position signal from a vehicle throttle 38, and provides control signals to the engine 12 for engine speed and torque related control and signals to the transmission 14 for shift related control. Additionally, depending on the selected engine speed and transmission gear, the controller 36 provides a signal (i.e. a TCC pressure command) on line 40 to the TCC 22 to set the desired torque converter slip. A sensor 42 measures the output behavior of the transmission 14. In one exemplary embodiment, the sensor 42 measures the rotational speed of the output shaft 28 of the transmission 14 and sends a speed signal to the controller 36. Exemplary sensors include an encoder, speed sensor, accelerometer, torque sensor, etc.
The controller 36 may take any suitable form including various combinations of one or more Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other suitable components to provide the described functionality. The controller has a set of control algorithms, including resident software program instructions and calibrations stored in memory and executed to provide the desired functions. The algorithms are preferably executed during preset loop cycles. Algorithms are executed, such as by a central processing unit, and are operable to monitor inputs from sensing devices and other networked controllers, and execute control and diagnostic routines to control operation of actuators. Loop cycles may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.
The present disclosure includes methods for adjusting the torque converter slip in response to changes in engine speed and/or transmission gear and/or engine torque so that the slip is at a desired minimum to conserve fuel, but is not in a potential crash condition or not so low where engine pulses and other noise signals are transferred through the torque converter 18 to the driveline 30 and are felt by vehicle occupants. The controller 36 selects the particular slip and transmits a corresponding TCC pressure command to the TCC 22 on line 40 for the current engine speed, transmission gear and engine torque based on a pre-populated table that is stored in the controller 36 as a result of vehicle testing or other operations for a minimum torque converter slip that provides good fuel economy and reduced vibration transfer. One process for populating such a table can be found in U.S. patent application Ser. No. 12/043,499, filed Mar. 6, 2008, commonly assigned to the assignee of the present application, and incorporated herein by reference. If the selected torque converter slip for a particular engine speed, transmission gear and engine torque does not provide the desired slip for preventing vibrations from being transferred to the driveline 30, then the signal from the sensor 42 is used to determine the vibrations in the controller 36, which can then increase the torque converter slip if the vibrations exceed a predetermined threshold.
Torque converter slip can be controlled by application of the TCC. The TCC includes structures mechanically, electronically, or fluidically operated to controllably couple the impeller and turbine of the torque converter, modulating an allowed slip therebetween. When the TCC is fully released, the fluidic coupling of the impeller and the turbine establish slip. When the TCC is fully locked, no slip between the impeller and turbine is possible. In one exemplary control method, the TCC fluid pressure is controlled so that the torque converter slip approaches a desired value. By reducing the pressure of the hydraulic fluid in the TCC, torque converter slip for a given operating condition will increase. Similarly, by increasing the pressure of the hydraulic fluid in the TCC, torque converter slip for a given operating condition will decrease.
As described above, increases in engine speed and/or torque can result in torque slip changing from a controlled value to an excessive value that must be controlled back to a controlled value. Such rapid changes in torque can result from throttle demands by the operator. Similarly, such changes can result from automatically generated commands, for example, in connection with cruise control functions or transmission shifts. Any rapid or sudden change in engine torque includes the potential to create a corresponding increase in torque converter slip. By monitoring engine torque commands or factors indicative of rapid increases in engine torque, methods can be employed to compensate for anticipated increased slip.
A control system can react to rapid increases in torque converter slip by reducing torque converter slip. Methods of feedback control are known in the art that can be used to control slip. Such methods monitor a desired value, control an output according to the desired value, and utilize a resulting value of the controlled output to subsequently improve control to the desired value. Feedback control is known to control slip in a torque converter through variable control of TCC pressure. A desired torque converter slip can be monitored, a TCC pressure command can be modulated in order to control resulting torque converter slip, and the resulting torque converter slip can be used in a feedback loop to subsequently modulate the TCC pressure command. In this way, feedback control can be utilized to control torque converter slip to a desired value. The desired value can be a steady state term, substantially unchanging through a time period, or the desired value can be transitory, for example, increasing or decreasing through a period or changing according to a step profile. Additionally, methods of feed forward control are known, utilizing predictions of control requirements to preemptively issue commands based upon the predictions. Both feedback control and feed forward control can be utilized to react to increases in torque converter slip.
Such an exemplary system can include a pressure control term described by the following equation.
TCCpressure command=feedback_term+feed_forward_term 
The feed forward term can be based upon many different factors affecting torque applied through the torque converter. In one exemplary embodiment, the feed forward term is based upon engine torque, with the feed forward term increasing with increasing engine torque.
As described above, methods are known to reestablish control over torque converter slip after an unintended change in slip. In addition, a decrease in torque converter slip through known methods to reestablish control over torque converter slip frequently overshoot the desired slip value and drive the torque converter slip to a zero value or crash, resulting in adverse impacts to drivability, as described above. It is known in the art that unexpected changes in slip are caused, for example, by unintended changes in engine torque, vehicle output disturbances (road bumps), and TCC pressure disturbances (pump pressure disturbances).
Methods to reduce or control slip after an increase are contemplated and disclosed herein utilizing feed forward and feedback control. However, these methods rely upon accurate and timely measurements of operation of the powertrain to accurately control the slip. As is known in the art, a number of sources of inaccuracy and interference can disrupt the accurate and timely measurement of the operation. Sources of inaccuracy include factors such as physics of the employed sensor, asynchronicity between the measured engine and turbine speeds, electromagnetic interference, vehicle vibrations, numerical round-errors, and sensor resolution.
Methods of statistical analysis are known to analyze behavior of a system and unknowns acting upon the system and provide probability based descriptions of the system. Statistical methods can be applied to operation of a TCC and utilized to determine a likely crashed condition of the torque converter or a corresponding likely locked condition of the TCC. A method is disclosed to quickly and accurately diagnose a likely condition of the torque converter based upon statistical analysis of the clutch is disclosed such that a crash condition can be recovered from or avoided.
A number of statistical methods of analyzing a TCC are envisioned. For example, a probability that slip at the TCC is zero or below a low slip threshold, indicating the torque converter to be at or near a crashed condition, can be determined. A probability that the TCC is currently locked can be expressed by the following equation.
Such a probability can be utilized to diagnose the crashed condition, for example, by comparison to a threshold probability calibrated to accurately diagnose the condition. Similarly to Equation 2, a probability that the TCC is in a slipping condition or is not locked can be expressed by the following equation.
The value k describes each variable as a measured value at the k sample value in a series of sample values. The value yk is the measured value of the TCC slip. The subscripts 0 and 1 refer to the system as described by model 0 or 1. The above embodiments of models 0 and 1 describe a locked TCC and a slipping TCC, respectively, but it will be appreciated that different formulas or expressions can similarly be utilized to describe any two conditions being diagnosed in a TCC. P0,k and P1,k represent the system's statistical property named covariance or square of the standard deviation at time k. The variable yref,k describes the reference slip value at time k, selected as a reference value indicating the slip to be at a slip value indicating or describing the TCC to not be in a locked condition. For example, the reference slip can be set to a desired slip level, or the reference slip can be set to a minimum level indicating a non-crashed condition. One having skill in the art will appreciate that exemplary Equation 2 differs from exemplary Equation 3 by setting yref,k equal to 0. Different models could be selected with the reference slip values selected to diagnose operation of the system depending upon the particular reference values. H0 and H1 refer to the hypothesis that the system can be described by model 0 or 1, respectively. The probabilities represented can be determined iteratively through a number of samples. Through Equations 2 and 3, probabilities can be determined that describe whether the TCC is locked or not locked. These equations can be compared to each other to describe a likelihood ratio that the clutch is in an unlocked state. Such a likelihood ratio can be expressed by the following equation.
In this equation, a ratio of less than one describes a TCC that is more likely to be locked than unlocked, whereas a ratio of greater than one describes a TCC that is more likely to be unlocked than locked. Statistical analysis of the ratio expressed by Equation 4 can be utilized to determine whether it is more likely than not that the torque converter is in a crashed condition. Exemplary methods are disclosed herein for determining whether the torque converter is in a crashed condition, but one having skill in the art will appreciate that a number of known methods are possible to analyze results of the ratio above over time.
The probability equations described above, Equations 2 and 3, utilize standard deviation terms.
The ratio of Equation 4 can be utilized directly to describe a likely condition of the torque converter or the corresponding TCC. However, variation in the probability terms of the ratio will create a change in the likelihood ratio proportional to the changes in the probability terms. Mathematical operations to improve resolution in a signal output are known. For example, one having ordinary skill in the art will appreciate that utilizing a base 10 logarithmic operation upon a value centering on a value of one can be utilized to transform the value depending upon whether the value is above or below one. The sign of the resulting value changes depending upon whether the input is above or below one. The logarithmic function is used is to simplify the mathematical expression and facilitate the calculation of the ratio. The logarithmic function is used because it is a monotonically increasing function preserving the information found in Equation 4. As a result, an expression log Λk (yk) can be utilized to return an exponentially increasingly negative value as the ratio value varies from one toward zero. In this way, as the probability of a crashed condition in the clutch increases, the resulting signal resulting from the logarithmic operation returns a significantly decreasing value.
The methods described above to statistically determine a condition of the clutch can be used in single measurements. However, the variables utilized to determine the probabilities in the ratio are subject to signal noise. As a result, individual measurements can be unreliable in order to indicate and react to a locked clutch condition. Instead, the probabilities at each time sample, k, can be combined to filter or minimize the effects of noise over a period of sample values. One exemplary form of such an operation can be expressed by the following equation.
One to k represents a summing sample period through which values are collected into a series to be summed for the test statistic. Through this equation, assuming the sample of values from one to k to be sufficiently large, the effects of signal noise in the signal are minimized. A small number of values indicating a crashed condition caused by noise in the monitored data will not indicate a crashed condition, but repeated values indicating a crashed condition will affect the test statistic to describe a crashed condition. However, one having skill in the art will appreciate that the sample of values from one to k must also not be too large, as the resulting test statistic must relatively quickly respond to repeated negative values to indicate the crashed condition in a timely manner.
Tracking a series of values of the above described ratio or a test statistic manipulating the values of the above ratio indicating a crashed condition in the torque converter can be accomplished by a number of methods known in the art. For example, values of the ratio or values of the exemplary test statistic can be analyzed through further statistical methods known in the art to determine an occurrence and magnitude of the negative values generated. Another exemplary method is to sum test statistic values and compare the sum to a threshold value indicating a sufficiently negative sum to indicate a crashed condition in the clutch.
One having skill in the art will appreciate that the accumulation of test statistic values depicted in
The methods described above indicate a TCC with zero slip or a corresponding crashed condition in the torque converter. Indication of the crashed condition can be used to react to the undesirable crashed condition. For example, it will be appreciated that control of the TCC can be modulated to increase an amount of slip allowed in the torque converter. For example, in the exemplary clutch configuration described above wherein a pressure command to the clutch is utilized to modulate slip within the torque converter, a predetermined drop to the pressure command can be utilized to recover or increase slip from the crashed condition. The predetermined drop may be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict operation of the torque converter, and a plurality of predetermined drops can be utilized depending upon engine speed, vehicle speed, transmission gear, the magnitude of slip being controlled in the torque converter, or other factors affecting operation of the torque converter and the occurrence of crash conditions therein. A single drop in pressure command can be utilized to react to a crashed condition in the torque converter. In the alternative, an initial drop in pressure command can be utilized, and, in combination with continued monitoring of the crashed condition according to methods described herein, a subsequent series of drops can be commanded until the monitoring indicates that the crashed condition has been resolved. In the alternative, instead of a step drop or a series of step drops in pressure command, a pressure drop profile can be utilized. For example, upon indication of crashed condition, a controlled drop in pressure command can be generated until continued monitoring of the clutch indicates that the crashed condition has been resolved. Many embodiments of reactions to the indication of the crashed condition are envisioned, and the disclosure is not intended to be limited to the particular exemplary embodiments described herein.
As mentioned above, it will be appreciated that Equations 2 and 3 describe a specific set of reference slip speeds including a zero slip speed indicating a crashed condition and a non-zero slip speed indicating normal operation of the torque converter in a controlled slip mode. Such a non-zero slip speed indicating normal operation of the torque converter will be different for different particular torque converters and can be selected according to methods known in the art. As described above, occurrence of a crashed condition is frequently undesirable, creating adverse effects to drivability. In one embodiment, a non-zero low slip threshold can be selected to indicate a threshold low slip condition, which when indicated can be used to control increased slip in order to avoid a potential crash condition. This low slip threshold is selected to adequately predict impending crash conditions without indicating excessive false indications and may be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict torque converter operation, and a multitude of thresholds might be used by the same powertrain depending upon engine speed, vehicle speed, transmission gear, the magnitude of slip being controlled in the torque converter, or other factors affecting operation of the torque converter and the occurrence of crash conditions therein. Based upon this low slip threshold, methods employed above, for example, utilizing iterative sums of the ratio described above, can be used to initiate commands to avoid the crash condition, for example, by commanding a step decrease to pressure commands to the TCC. Utilizing a reference slip of zero or a low value selected as a low slip threshold, statistical analysis of the clutch can be performed to diagnose the condition of the TCC and generate commands to recover from or avoid a crash condition.
Further, the methods described herein discuss an embodiment controlling slip if the statistical analysis describes the slip as being close to or at a crash condition. It will be appreciated that similar methods can be employed to determine a likely threshold high slip condition, comparing versions of Equations 2 and 3 based upon a reference slip speed normal operation of the torque converter in a controlled slip mode and a threshold high slip speed to determine occurrence of a threshold high slip condition. Such a threshold high slip speed can be selected to describe a condition of unacceptably high slip according to methods similar to those described above for selecting the low slip threshold. Statistical analysis of the slip speed can simultaneously be operated for identification of a threshold low slip speed and a threshold high slip speed, and the slip speed can be controlled according to whether either threshold is likely violated. In an alternative method, the summed value described in
An exemplary process is disclosed to indicate either a threshold high slip condition or threshold low slip condition.
The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
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|Clasificación de EE.UU.||701/301, 701/51, 192/3.3, 192/3.29, 477/175, 477/169, 477/64, 477/176, 477/62, 475/118, 192/103.00R|
|Clasificación cooperativa||Y10T477/735, Y10T477/635, Y10T477/755, Y10T477/753, Y10T477/6352, F16H2061/145, F16H2059/467, F16H61/143|
|19 Mar 2010||AS||Assignment|
Owner name: GM GLOBAL TECHNOLOGY OPERATIONS, INC., MICHIGAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:OTANEZ, PAUL G.;LEE, CHUNHAO J.;SAMIE, FARZAD;SIGNING DATES FROM 20100104 TO 20100112;REEL/FRAME:024108/0783
|8 Nov 2010||AS||Assignment|
Owner name: WILMINGTON TRUST COMPANY, DELAWARE
Free format text: SECURITY AGREEMENT;ASSIGNOR:GM GLOBAL TECHNOLOGY OPERATIONS, INC.;REEL/FRAME:025327/0156
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|10 Feb 2011||AS||Assignment|
Owner name: GM GLOBAL TECHNOLOGY OPERATIONS LLC, MICHIGAN
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Owner name: GM GLOBAL TECHNOLOGY OPERATIONS LLC, MICHIGAN
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